December 2002
Intermediate to advanced
1232 pages
56h 38m
English
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Sidestep Slow Hosts
A slow host is one that requires more than a few seconds to accept delivery of a modestly sized email message. To illustrate, consider the following example produced by a verbose transaction of sending email to such a slow host:
% /usr/sbin/sendmail -v -Rslowhost.com -q
Running /var/spool/mqueues/q.2/df/f0DHnvO02567 (sequence 1 of 1)
bob@slowhost.com... Connecting to mx.slowhost.com. via esmtp...
220 mx.slowhost.com ESMTP Sendmail 8.10.1/8.10.1; Fri, 13 Dec 2002 10:50:20 -0700
(MST)
>>> EHLO mx.slowhost.com
250-mx.slowhost.com Hello you@yourhost.com [123.45.678.9], pleased to meet you
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-SIZE
250-DSN
250-ONEX
250-ETRN
250-XUSR
250 HELP
>>> MAIL From:<you@yourhost.com> SIZE=16
...
You wait 2 minutes for slowhost to look you up.
...This situation can get worse, especially if the slow site runs slow antispam software, because that site can take 9 or 10 minutes to validate you. This can cause sendmail to seem to hang for 9 or 10 minutes, then suddenly to continue with:
250 2.1.0 <you@yourhost.com>... Sender ok >>> RCPT To:<bob@slowhost.com> 250 2.1.5 <bob@slowhost.com>... Recipient ok >>> DATA 354 Enter mail, end with "." on a line by itself >>> .
Furthermore, some mail transfer agents (MTAs) start to place a message on disk only after all the data has been received, so writing to an NFS-mounted disk can appear to hang for several seconds:
250 2.0.0 f0DHoNh91321 Message accepted for delivery bob@slowhost.com... Sent (f0DHoNh91321 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.